The present invention generally relates to radiocommunication systems and methods for signalling in radiocommunication systems and, more particularly, to systems and methods for sending messages using a digital control channel in such systems.
One radiocommunication system is described by the GSM, a European standard for radiocommunication which is intended to provide uniformity so that users can access radiocommunication systems throughout Europe with minimal equipment compatibility problems. The GSM includes specifications for many types of subscriber services, including a message function service called the Short Message Service (SMS) which provides for the transmission of messages having up to 160 alphanumeric characters to be sent to a subscriber at his or her remote unit. These messages originate, for example, from mobile units transmitting them to a service center for subsequent transmission to the designated subscriber ("mobile-originated") or from any wire-based system simply by calling an operator at the service center who types the message into the system ("mobile-terminated").
However, the short message service of GSM suffers from many drawbacks and limitations and, accordingly, has not been universally accepted or implemented in other systems, for example the North American digital radiocommunication system standardized as IS-54B.
For example, security for the short message service is almost non-existent in the GSM. Although the SMS enjoys the same authentication protection which is provided to other messages transmitted over the air interface using, for example, the mobile identification number (MIN) and/or the electronic serial number (ESN), to ensure that messages are received only by the intended remote unit, such authentication procedures provide no protection for short messages once they have been received by the intended remote unit. Thus, these messages are readily displayable, or otherwise reviewable, by any individual using the remote unit. In the event that, for example, a subscriber loans his or her remote unit to another individual, it may be undesirable for these messages to be so readily obtainable.
Other features are also lacking in the GSM message service. For example, mechanisms for delaying delivery of the message, urgency indications, user acknowledgment, sufficient addressing capability, and validity periods for delivery are not found in the GSM.